Well-known catalysts for acrylonitrile synthesis synthesize acrylonitrile from propylene in a fluid bed ammoxidation process and so forth, and many proposals have been made regarding such catalysts, which are presently used in industry worldwide.
For example, Japanese Patent Application, Second Publication No. S61-13701, Japanese Patent Application, First Publication No. S59-204163, Japanese Patent Application, First Publication No. H1-228950, Japanese Patent Application, First Publication No. H10-43595, Japanese Patent Application, First Publication No. H10-156185 and U.S. Pat. No. 5,688,739 (hereinafter, expressed as prior art document group 1) disclose a catalyst composed mainly of molybdenum and bismuth. Further, Japanese Patent No. 3217794 discloses a method to maintain acrylonitrile yield at a high level for a long time by keeping the atomic ratio of molybdenum to other metal components in the bulk composition of the catalyst within a certain range, in the case of producing acrylonitrile in a fluid bed using a catalyst containing molybdenum.
However, prior art document group 1 intended mainly to improve so-called catalyst initial characteristics such as activity, selectivity, etc. by specifying catalyst component elements and their bulk compositional ratios and there was no reference to catalyst structural design technology to maintain catalytic activity and selectivity at a high level for a long time. On the other hand, Japanese Patent No. 3217794 discloses a method to maintain acrylonitrile yield at a high level for a long time, however, performing the disclosed method alone is insufficient to attain this goal and further improvement is necessary from the industrial point of view.